The present invention relates to a coffee brewing apparatus comprising a filter chamber for brewing coffee, a water tank, a heater for heating water delivered from the water tank and providing hot water to the filter chamber, and a power switch.
A coffee brewing apparatus provided with a mill to grind coffee beans is known, and that kind of apparatus with a timer is disclosed in Japanese Utility Model Publication No. 61-5215. The operation of this apparatus will be explained with reference to FIG. 3.
The current time and desired activation time are set by means of a fast-traverse button 34 or a slow-traverse button 35 together with a time setting button 36. Then, when a main switch 37 is toggled from "OFF" position to "TIMER" position, the coffee brewing apparatus gets into the timer mode. If a mill switch is depressed during the timer mode, mill 28 is energized causing coffee beans to be ground resulting in coffee powder. When the current time coincides with the activation time, power is supplied to a heater and water contained in water tank 27 is heated. Coffee beverage is brewed by transmitting hot water through the coffee powder ground by mill 28. The brewed coffee is poured into the coffee vessel 31 from upper protrusion 29. Then, a heating plate contained in base 30 keeps the coffee warm.
However, the coffee taste deteriorates due to oxidization if the coffee is warmed for a long time. Therefore, the known coffee brewing apparatus automatically ceases to supply power to the heating plate following the operation of the timer of the apparatus if a predetermined time (59 minutes) lapses after brewing.
The main switch employed in the known coffee brewing apparatus is a dual three-contact switch which can take three positions: "TIMER", "OFF" or "ON". While the switch is in the "ON" position, power is always supplied to the heater. If the switch is turned to the "OFF" position, the power source is switched off.
In addition to this kind of a dual three-contact switch, a tumbler switch, a push-button switch or a switch having a timer function realized by a spiral spring, are conventionally utilized as a power switch of the coffee brewing apparatus. However, in case such a switch is employed the power source has to be turned off by hand.
Generally, a thermostat is arranged between the heater and the power lines in order to keep the heater temperature within a limited range. The circuit is turned on by this thermostat if the temperature falls below a preselected temperature, for example 90.degree. C., and is turned off if it rises above another preselected temperature, for example 120.degree. C. Furthermore, the coffee brewing apparatus is generally provided with a thermal fuse near the heater in order to prevent the situation in which the thermostat does not turn off the heater even if the temperature rises above the preselected maximum temperature and the heater continues to be heated.
In the coffee brewing apparatus shown in the above-mentioned Utility Model Publication No. 61-5215, the power to the heater is automatically cut-off by a timer after a predetermined time elapses. In a conventional coffee brewing apparatus, when a heating plate is heated excessively, the melting of a thermal fuse cuts-off the power supply to the heater. However, in the case of the known apparatus, power continues to be supplied to the electric portion of the apparatus other than the heater portion so that the electrical portion still might cause a fire. Therefore, in the known coffee brewing apparatus, each time that power is no longer supplied to the heater, or each time that an abnormal situation happens, the user must turn off the power switch manually in order to remove the possibility of having a fire.
Furthermore in the known apparatus, if a motor is heated abnormally or excessively due to overload and the operator does not recognize the abnormal situation, the motor will be burned out.